Newsgroups: rec.backcountry
\nFrom: eugene@amelia.nas.nasa.gov (Eugene N. Miya)
\nSubject: [l\/m 9\/25\/92] Water filters & Giardia\tDistilled Wisdom (9\/28) XYZ
\nOrganization: NAS Program, NASA Ames Research Center, Moffett Field, CA
\nDate: Sat, 9 Jan 93 12:20:20 GMT
\nMessage-ID:
\nReply-To: tut@sun.com (Bill Tuthill)
\nLines: 1461<\/p>\n
Panel 9<\/p>\n
Index:
\n\ta. (Title?)
\n\t [Comparison of filters, boiling and iodine]<\/p>\n
\t Filters: First Need, Katadyn,
\n\t Boiling,
\n\t Iodine: PolarPure, Potable-Aqua<\/p>\n
\t Bill Tuthill
\n\t 1991 – 1992<\/p>\n
\t Based on “Medicine for Mountaineering”, owner’s manuals and
\n personal experience of author<\/p>\n
\tb. GIARDIASIS
\n\t Memo from Center from Disease Control
\n\t Dennis D. Juranek
\n\t Chief, Epidemiology Activity
\n\t Parasitic Diseases Branch
\n\t Division of Parasitic Diseases
\n\t Centers for Disease Control
\n\t 1990<\/p>\n
\tc. Back-country water treatment to prevent giardiasis.
\n\t American Journal of Public Health
\n\t December 1989, Vol 79, No 12, pp 1633-1637.
\n\t Copyright 1989 AJPH 0090-0036\/89$1.50 [used without permission]
\n\t Filters: First Need, H2OK, Katadyn, Pocket Purifier, Water Purifier
\n\t Chemicals: Polar Pure, Coghlan’s Emergency Germicidal Drinking
\n\t Water Tablets, Potable Aqua, 2% iodine,
\n\t Sierra Water Purifier, Halazone, commercial liquid bleach
\n\t Jerry E. Ongerth, PhD, PE,
\n\t Ron L. Johnson,
\n\t Steven C Macdonald, MPH,
\n\t Floyd Frost, PhD,
\n\t Henry H. Stibbs, PhD<\/p>\n
\td. REI Water Filter Chart (2 similar articles)
\n\t Comparison of specs: pore size, weight, capacity, filter life,
\n\t cost\/gallon, price, replacement cost,
\n \t\t\t\telements
\n\t Filters: Katadyn, MSR, PUR, First Need, Basic Designs, Timber Line<\/p>\n
\t 199x?<\/p>\n
Copyright (c) 1991 by Bill Tuthill<\/p>\n
Unpurified drinking water may contain four things that pose health risks:
\nprotozoan parasites (e.g. giardia), toxic bacteria, harmful viruses, and
\npoisonous chemicals. Of the methods available in the field, only boiling
\nand iodine are entirely effective against the first three, and only charcoal
\nfiltration is effective against the fourth.<\/p>\n
The First Need(R) water filter is cheap (less than $40), but is effective
\nmerely against protozoan parasites. Its .4 micron filter pores are smaller
\nthan giardia cysts at 3.5 microns, but larger than some bacteria, such as
\nE. coli at .3 to .9 microns. The First Need’s charcoal canister is not big
\nenough to be effective against poisonous chemicals — you need a pound of
\ncharcoal for this — so it just adds unnecessary weight, and provides a
\npotential haven for the growth of harmful bacteria. If you own a First Need
\nfilter, flush it with iodine after each trip.<\/p>\n
The Katadyn(R) water filter is expensive (over $200), but is completely
\neffective against bacteria as well as giardia. Moreover, it can be cleaned
\nafter it clogs up. The Katadyn is effective at removing smaller bacteria
\nsuch as E. coli. However, its .2 micron filter is not effective against
\nany virus. If you travel abroad (to Nepal for example), you risk viral
\ninfections such as Hepatitis A and Hepatitis non-A non-B, among others.<\/p>\n
MSR has a new water filter, which may be superior to the Katadyn. Results
\nfrom the field aren’t in yet.<\/p>\n
To be entirely safe, water should be boiled for at least five minutes.
\nGiardia is killed in less than a minute at 176 degrees, well under the
\nboiling point. Bacteria and viruses last somewhat longer, but are probably
\nkilled in less than five minutes at 190 degrees. Some viruses may last
\nlonger; nobody knows. At 10,000 feet water boils at 194 degrees; above
\nthis altitude boil water about an extra minute for each 1000 feet.<\/p>\n
If you have neither the time nor the inclination to boil water, iodine
\nis equally effective. After 15 minutes (30 minutes for very cold water),
\na sufficient dose of iodine kills all protozoa, bacteria, and viruses.
\nOne readily-available choice is Potable-Aqua(R) tablets. Dissolve one
\ntablet per liter of water (two tablets if cloudy) and wait. The problem
\nwith iodine tablets is that they degrade upon contact with moisture, so
\nkeep that bottle dry, and discard it upon returning home.<\/p>\n
Avoid halazone and Clorox, because chlorine is volatile, slow to disinfect,
\nand works differently against protozoa and viruses at various pH levels.
\nIt also reacts with organic compounds to form carcinogenic chloramines.<\/p>\n
Iodine is not highly toxic, and in fact is an essential ingredient of
\nhuman nutrition. However, continuous ingestion of large doses may cause
\nhealth problems, so don’t iodinate all your water for more than a few
\nmonths at a time.<\/p>\n
The accepted concentration for iodine disinfection is 8 milligrams per
\nliter, but this is mostly to get rid of protozoan parasites. A good way
\nto reduce overall iodine consumption and minimize that iodine flavor is
\nto filter first, then use a low concentration of iodine to get rid of
\nbacteria and viruses. For this, a concentration of .5 mg\/L is deemed
\nadequate, so one capful of PolarPure or one Potable-Aqua tablet should
\ndisinfect around 16 liters of lightly filtered water. The Timberline(R)
\nfilter, with its 2 micron pores, is fine for removing protozoa.<\/p>\n
Giardia has become a well-known, almost fashionable, outdoor hazard.
\nMany people who experience gastro-intestinal problems after drinking
\nbad water think they have contracted giardia. In many cases they have
\ncontracted something else. Since the only FDA-approved treatment for
\ngiardia (Flagyl) is very nasty, it’s wise to make sure you really have
\ngiardia before taking Flagyl. Most low-grade bacterial infections go away
\non their own, and Flagyl is ineffective against viral infections. One
\nalternative to Flagyl is quinacrine. In many parts of the world (Asia
\nfor example) Tinidazole is available, and is preferable to Flagyl because
\nit is less toxic and quicker acting.<\/p>\n
[This information based on “Medicine for Mountaineering”, various owner’s
\npamphlets, and personal experience.]<\/p>\n
Addedum 1992<\/p>\n
A packet of information arrived recently from Recovery Engineering
\nin Minneapolis, which I’ll summarize as promised.<\/p>\n
They have a new product, the Pur Scout, which I believe is destined
\nto replace the First Need as the most popular low-cost filter. It
\nhas the same 1 micron filter plus iodine matrix as the Pur Explorer,
\npumps a quart in 120 seconds, but weighs only 12 oz! Capacity is
\n200 gallons, twice the First Need, but its $60 cost is less than
\ntwice as much. The Scout is not self-cleaning like the Explorer,
\nand is only half the speed, with 2\/5 the filter life.<\/p>\n
Unlike other water filters, all Pur products meet EPA’s purification
\nguidelines. No other filter does this, because no other filter can
\nremove viruses. Here is the abstract from a study done at U Arizona
\non the Pur Tritek(tm) system:<\/p>\n
\t“Three identical [Pur Traveller water filters] were evaluated
\n\tfor their ability to inactivate\/remove Klebsiella terrigena,
\n\tpoliovirus type1, rotavirus SA-11, and Giardia lamblia cysts.
\n\tThe units were operated according to the manufacturer’s
\n\tinstructions until the designed lifetime of 100 gallons (378
\n\tliters) passed through. The units were challenged with [the
\n\tmicro-organisms mentioned above] after a passage of 0, 50, 75
\n\tand 100 gallons. At the 75% lifetime challenge, ‘worst case’
\n\twater quality of 1500 mg\/l dissolved solids, 10 mg\/l organic
\n\tmatter, 4 degrees C, with a turbidity of 30 NTU and a pH of 9
\n\twas used. For the 100% lifetime test the worst case water
\n\tquality at pH 5 was used. The units were also tested after
\n\tstagnation for 48 hours at the 50%, 75%, and 100% [stages].<\/p>\n
\t“At 0 and 50% lifetime test points, > 99.9999% of the bacteria,
\n\t> 99.9% of the Giardia cysts, and > 99.99% of the test viruses
\n\twere removed. With worst case water two passages of the test
\n\twater through the units was required to achieve these same
\n\tremovals. These units would comply with criteria guidelines
\n\tsuggested by the US EPA…<\/p>\n
\t“One passage of the pH 9 worst case water was not sufficient
\n\tto remove the Klebsiella terrigena and poliovirus type1 to
\n\tthe required reduction. However, the required reduction [was]
\n\tachieved by passage of the test water through the units a
\n\tsecond time… Holding the water for 5 to 10 minutes after
\n\tit had passed through the units also resulted in a further
\n\treduction of test bacteria and viruses.”<\/p>\n
What is Klebsiella terrigena anyway? I assume it’s a bacteria, but
\nwhat disease does it cause? And what does NTU stand for? Also, is
\nparts per million (ppm) the same as milligrams per liter (mg\/l)?
\nHere is the residual iodine in ppm after treatment:<\/p>\n
\tcup1\tcup2\tcup3
\n 0%\t.7\t.7\t.7
\n 50%\t.6\t.5\t.6
\n 75%\t.6\t.6\t.7
\n100%\t.7\t.6\t.8<\/p>\n
This indicates that the filter still had plenty of life at 100 gallons.
\nIt also indicates that there is enough residual iodine to kill off all
\nviruses and bacteria overnight (assuming ppm = mg\/l). At these levels
\nsome iodine taste may be present, which can be removed with the optional
\ncharcoal filter. Since the charcoal filter also removes iodine, it
\nwould be prudent to use it only when filtering good quality water above
\n5 degrees C. It’s a tradeoff, though: when travelling thru agricultural
\nareas, charcoal filtration helps remove pesticides and herbicides.<\/p>\n
All in all, I’ve decided to trade in my Katadyn for a Pur Explorer. I
\nused an MSR last week on the Rogue, and liked its pump action and bottle
\nattachment, but it *did* start to clog. Anybody want to buy my Katadyn
\n(in excellent condition) for a mere $185? F*ck the Swiss.<\/p>\n
=====<\/p>\n
OCR’ed memo from the Center from Disease Control:<\/p>\n
GIARDIASIS<\/p>\n
GIARDIASIS: By Dennis D. Juranek, Chief, Epidemiology Activity
\nParasitic Diseases Branch
\nDivision of Parasitic Diseases
\nCenters for Disease Control<\/p>\n
Transmission and Control<\/p>\n
Introduction<\/p>\n
During the past fifteen years giardiasis has been recognized as one of the
\nmost frequently occurring waterborne diseases in the United States (1).
\nGiardia lamblia have been discovered in the United States in places as far
\napart as Estes Park, Colorado (near the Continental Divide); Missoula,
\nMontana; Wilkes-Barre, Scranton, and Hazleton, Pennsylvania; and Pittsfield
\nand Lawrence, Massachusetts just to name a few. In light of recent large
\noutbreaks of waterborne giardiasis, it seem timely to present reliable
\ninformation on the way in which giardiasis is acquired, treated, and
\nprevented.<\/p>\n
Giardiasis: Prevalence and Symptoms<\/p>\n
Giardiasis is a disease caused by a one-celled parasite with the scientific
\nname Giardia lamblia. The disease is characterized by intestinal symptoms
\nthat usually last one week or more and may be accompanied by one or more of
\nthe following: diarrhea, abdominal cramps, bloating, flatulence, fatigue, and
\nweight loss (see Table 1). Although vomiting and fever are listed in Table 1
\nas relatively frequent symptoms, they have been uncommonly reported by people
\ninvolved in waterborne outbreaks of giardiasis in the United States. Table 1
\nalso suggests that 13 percent of patients with giardiasis may have blood in
\ntheir stool. Giardia, however, rarely causes intestinal bleeding. Therefore,
\nblood in the stool of a patient with giardiasis almost always indicates the
\npresence of a second disease.<\/p>\n
While most Giardia infections persist only for one or two months, some people
\nundergo a more chronic phase, which can follow the acute phase or may become
\nmanifest without an antecedent acute illness. The chronic phase is
\ncharacterized by loose stools, and increased abdominal gassiness with
\ncramping, flatulence and burping. Fever is not common, but malaise, fatigue,
\nand depression may ensue (2). For a small number of people, the persistence of
\ninfection is associated with the development of marked malabsorption and
\nweight loss (3). Similarly, lactose (milk) intolerance can be a problem for
\nsome people. This can develop coincidentally with the infection or be
\naggravated by it, causing an increase in intestinal symptoms after ingestion
\nof milk products.<\/p>\n
Some people may have several of these symptoms without evidence of diarrhea or
\nhave only sporadic episodes of diarrhea every 3 or 4 days. Still others may
\nnot have any symptoms at all. Therefore, the problem may not be whether you
\nare infected with the parasite or not, but how harmoniously you both can live
\ntogether, or how to get rid of the parasite (either spontaneously or by
\ntreatment) when the harmony does not exist or is lost.<\/p>\n
Medical Treatment<\/p>\n
Three drugs are available in the United States to treat giardiasis: quinacrine
\n(Atabrine*), metronidazole (Flagyl*), and furazolidone (Furoxone*). All are
\nprescription drugs. In a recent review of drug trials in which the efficacies
\nof these drugs were compared, quinacrine produced a cure in 93% of 129
\npatients, metronidazole cured 92% of 219, and furazolidone cured 84% of 150
\npatients (4). Quinacrine is generally the least expensive of the anti-Giardia
\nmedications but it often causes vomiting in children younger than 5 years
\nold. Although the treatment of giardiasis is not an FDA-approved indication
\nfor metronidazole, the drug is commonly used for this purpose. Furazolidone
\nis the least effective of the three drugs, but is the only anti-Giardia
\nmedication that comes as a liquid preparation, which makes it easier to
\ndeliver the exact dose to small children and makes it the most convenient
\ndosage form for children who have difficulty taking pills. Cases of chronic
\ngiardiasis refractory to repeated courses of therapy have been noted, one of
\nwhich responded to combined quinacrine and metronidazole treatment (5).<\/p>\n
(*) Use of trade names is for purposes of identification only.<\/p>\n
Etiology and Epidemiology<\/p>\n
Giardiasis occurs worldwide. In the United States, Giardia is the parasite
\nmost commonly identified in stool specimens submitted to state laboratories
\nfor parasitologic examination. From 1977 through 1979, approximately 4% of 1
\nmillion stool specimens submitted to state laboratories were positive for
\nGiardia (6). Other surveys have demonstrated Giardia prevalence rates ranging
\nfrom 1 to 20% depending on the location and ages of persons studied.
\nGiardiasis ranks among the top 20 infectious diseases that cause the greatest
\nmorbidity in Africa, Asia, and Latin America (7); it has been estimated that
\nabout 2 million infections occur per year in these regions (8).<\/p>\n
People who are at highest risk for acquiring a Giardia infection in the United
\nStates may be placed into five major categories:<\/p>\n
1) People in cities whose drinking water originates from streams or
\n rivers and whose water treatment process does not include
\n filtration, or filtration is ineffective because of malfunctioning
\n equipment.
\n2) Hikers\/campers\/outdoorspeople.
\n3) International travelers
\n4) Children who attend day-care centers, day-care center staff, and
\n parents and siblings of children infected in day-care centers.
\n5) Homosexual men.<\/p>\n
People in categories 1, 2, and 3 have in common the same general source of
\ninfections, i.e., they acquire Giardia from fecally contaminated drinking
\nwater. The city resident usually becomes infected because the municipal water
\ntreatment process does not include a filter that is necessary to physically
\nremove the parasite from the water. The number of people in the United States
\nat risk (i.e., the number who receive municipal drinking water from unfiltered
\nsurface water) is estimated to be 20 million. International travelers may
\nalso acquire the parasite from improperly treated municipal waters in cities
\nor villages in other parts of the world, particularly in developing
\ncountries. In Eurasia, only travelers to Leningrad appear to be at increased
\nrisk. In prospective studies, 88% of U.S. and 35% of Finnish travelers to
\nLeningrad who had negative stool tests for Giardia on departure to the Soviet
\nUnion developed symptoms of giardiasis and had positive tests for Giardia
\nafter they returned home (10,11). With the exception of visitors to Leningrad,
\nhowever, Giardia has not been implicated as a major cause of traveler’s
\ndiarrhea. The parasite has been detected in fewer than 2% of travelers who
\ndevelop diarrhea. Hikers and campers risk infection every time they drink
\nuntreated raw water from a stream or river.<\/p>\n
Persons in categories 4 and 5 become exposed through more direct contact with
\nfeces of an infected person, e.g., exposure to soiled diapers of an infected
\nchild (day-care center-associated cases), or through direct or indirect
\nanal-oral sexual practices in the case of homosexual men.<\/p>\n
Although community waterborne outbreaks of giardiasis have received the
\ngreatest publicity in the United States during the past decade, about half of
\nthe Giardia cases discussed with staff of the Centers for Disease Control in
\nthe past 2 to 3 years have a day-care center exposure as the most likely
\nsource of infection. Numerous outbreaks of Giardia in day-care centers have
\nbeen reported in recent years. Infection rates for children in day-care
\ncenter outbreaks range from 21 to 44% in the United states and from 8 to 27%
\nin Canada (12,13,14,15,16,17). The highest infection rates are usually
\nobserved in children who wear diapers (l to 3 years of age). In one study of
\n18 randomly selected day care centers in Atlanta (CDC unpublished data), 10%
\nof diapered children were found infected. Transmission from this age group to
\nolder children, day-care staff, and household contacts is also common. About
\n20% of parents caring for an infected child will come infected.<\/p>\n
It is important that local health officials and managers of water utility
\ncompanies realize that sources of Giardia infection other than municipal
\ndrinking water exist. Armed with this knowledge, they are less likely to make
\na quick (and sometimes wrong) assumption that a cluster of recently diagnosed
\ncases in a city is related to municipal drinking water. Of course, drinking
\nwater must not be ruled out as a source of infection when a larger than
\nexpected number of cases are recognized in a community, but the possibility
\nthat the cases are associated with a day-care center outbreak, drinking
\nuntreated stream water, or international travel should also be
\nentertained.<\/p>\n
Parasite Biology<\/p>\n
To understand the finer aspects of Giardia transmission and the strategies for
\ncontrol, one must become familiar with several aspects of the parasite’s
\nbiology. Two forms of the parasite exist: a trophozoite and a cyst, both of
\nwhich are much larger than bacteria (see Figure 1). Trophozoites live in the
\nupper small intestine where they attach to the intestinal wall by means of a
\ndisc-shaped suction pad on their ventral surface. Trophozoites actively feed
\nand reproduce at this location. At some time during the trophozoite’s life,
\nit releases its hold on the bowel wall and floats in the fecal stream through
\nthe intestine. As it makes this journey, it undergoes a morphologic
\ntransformation into an egglike structure called a cyst. The cyst, which is
\nabout 6 to 9 micrometers in diameter x 8 to 12 micrometers (1\/100 millimeter)
\nin length, has a thick exterior wall that protects the parasite against the
\nharsh elements that it will encounter outside the body. This cyst form of the
\nparasite is infectious for other people or animals. Most people become
\ninfected either directly by hand-to-mouth transfer of cysts from the feces of
\nan infected individual, or indirectly by drinking feces-contaminated water.
\nLess common modes of transmission included ingestion of fecally contaminated
\nfood and hand-to-mouth transfer of cysts after touching a fecally contaminated
\nsurface. After the cyst is swallowed, the trophozoite is liberated through
\nthe action of stomach acid and digestive enzymes and becomes established in
\nthe small intestine.<\/p>\n
Although infection after the ingestion of only one Giardia cyst is
\ntheoretically possible, the minimum number of cysts shown to infect a human
\nunder experimental conditions is ten (18). Trophozoites divide by binary
\nfission about every 12 hours. What this means in practical terms that if a
\nperson swallowed only a single cyst, reproduction at this rate would result in
\nmore than 1 million parasites 10 days later, and 1 billion parasites by day 15.<\/p>\n
The exact mechanism by which Giardia causes illness is not yet well
\nunderstood, but is not necessarily related to the number of organisms
\npresent. Nearly all of the symptoms, however, are related to dysfunction of
\nthe gastrointestinal tract. The parasite rarely invades other parts of the
\nbody, such as the gall bladder or pancreatic ducts. Intestinal infection does
\nnot result in permanent damage.<\/p>\n
Transmission<\/p>\n
Data reported to the CDC indicate that Giardia is the most frequently
\nidentified cause of diarrheal outbreaks associated with drinking water in the
\nUnited States. The remainder of this article will be devoted to waterborne
\ntransmission of Giardia. Waterborne epidemics of giardiasis are a relatively
\nfrequent occurrence. In 1983, for example, Giardia was identified as the
\ncause of diarrhea in 68% of waterborne outbreaks in which the causal agent was
\nidentified (19). From 1965 to 1982, more than 50 waterborne outbreaks were
\nreported (20). In 1984, about 250,000 people in Pennsylvania were advised to
\nboil drinking water for 6 months because of Giardia-contaminated water.
\nMany of the municipal waterborne outbreaks of Giardia have been subjected to
\nintense study to determine their cause. Several general conclusions can be
\nmade from data obtained in those studies. Waterborne transmission of Giardia
\nin the United States usually occurs in mountainous regions where community
\ndrinking water is obtained from clear running streams, is chlorinated but is
\nnot filtered before distribution. Although mountain streams appear to be
\nclean, fecal contamination upstream by human residents or visitors, as well as
\nby Giardia-infected animals such as beavers, has been well documented. It is
\nworth emphasizing that water obtained from deep wells is an unlikely source of
\nGiardia because of the natural filtration of water as it percolates through
\nthe soil to reach underground cisterns. Well-water sources that pose the
\ngreatest risk of fecal contamination are those that are poorly constructed or
\nimproperly located. A few outbreaks have occurred in towns that included
\nfiltration in the water treatment process, but the filtration was not
\neffective in removing Giardia cysts because of defects in filter construction,
\npoor maintenance of the filter media, or inadequate pretreatment of the water
\nbefore it was filtered. Occasional outbreaks have also occurred because of
\naccidental cross-connections between water and sewerage systems.<\/p>\n
One can conclude from these data that two major ingredients are necessary for
\nwaterborne outbreak. First, there must be Giardia cysts in untreated source
\nwater and, second, the water purification process must either fail to kill or
\nfail to remove Giardia cysts from the water.<\/p>\n
Although beavers are often blamed for contaminating water with Giardia cysts,
\nit seems unlikely that they are responsible for introducing the parasite into
\nnew areas. It is far more likely that they are also victims: Giardia cysts
\nmay be carried in untreated human sewage discharged into the water by
\nsmall-town sewage disposal plants or originate from cabin toilets that drain
\ndirectly into streams and rivers. Backpackers, campers, and sports
\nenthusiasts may also deposit Giardia-contaminated feces in the environment
\nthat are subsequently washed into streams by rain. In support of this concept
\nis a growing amount of data that indicate a higher Giardia infection rate in
\nbeavers living downstream from U.S. National Forest campgrounds compared with
\na near zero rate of infection in beavers living in more remote areas.<\/p>\n
Although beavers may be unwitting victims in the Giardia story, they still
\nplay an important part in the transmission scheme, because they can (and
\nprobably do) serve as amplifying hosts. An amplifying host is one that is
\neasy to infect, serves as a good habitat for the parasite to reproduce, and,
\nin the case of Giardia, returns millions of cysts to the water for every one
\ningested. Beavers are especially important in this regard because they tend
\nto defecate in or very near the water, which ensures that most of the Giardia
\ncysts excreted are returned to the water<\/p>\n
The contribution of other animals to waterborne outbreaks of Giardia is less
\nclear. Muskrats (another semiaquatic animal) have been found in several parts
\nof the United States to have high infection rates (30 to 40%) (2l). Recent
\nstudies have shown that muskrats can be infected with Giardia cysts obtained
\nfrom humans and beavers. Occasional Giardia infections have been reported in
\ncoyotes, deer, elk, cattle, dogs, and cats, but not in horses and sheep,
\nencountered in mountainous regions of the United States. Naturally occurring
\nGiardia infections have not been found in most other wild animals (bear,
\nnutria, rabbit, squirrel, badger, marmot, skunk, ferret, porcupine, mink,
\nraccoon, river otter, bobcat, lynx, moose, bighorn sheep) (22).<\/p>\n
Removal from Municipal Water Supplies<\/p>\n
During the past 10 years, scientific knowledge about what is required to kill
\nor remove Giardia cysts from a contaminated water supply has increased
\nconsiderably. For example, it is known that cysts can survive in cold water
\n(4 deg C) for at least 2 months and that they are killed instantaneously by
\nboiling water (100 deg C) (23,24). It is not known how long the cysts
\nwill remain viable at other water temperatures (e.g., at 0 deg C or in a
\ncanteen at 15-20 deg C), nor is it known how long the parasite will survive
\non various environment surfaces, e.g., under a pine tree, in the sun,
\non a diaper-changing table, or in carpets in a day-care center. <\/p>\n
The effect of chemical disinfection, such as chlorine, on the viability of
\nGiardia cysts is an even more complex issue. It is clear from the number of
\nwaterborne outbreaks of Giardia that have occurred in communities where
\nchlorine was employed as a disinfectant that the amount of chlorine used
\nroutinely for municipal water treatment is not effective against Giardia
\ncysts. These observations have been confirmed in the laboratory under
\nexperimental conditions (25,26,27). This does not mean, however, that chlorine
\ndoes not work at all. It does work under certain favorable conditions.
\nWithout getting too technical, one can gain some appreciation of the problem
\nby understanding a few of the variables that influence the efficacy of
\nchlorine as a disinfectant.<\/p>\n
1) Water pH: at pH values above 7.5, the disinfectant capability of
\n chlorine is greatly reduced.
\n2) Water temperature: the warmer the water, the higher the efficacy.
\n Thus, chlorine does not work well in ice-cold water from mountain
\n streams.
\n3) Organic content of the water: mud, decayed vegetation, or other
\n suspended organic debris in water chemically combines with chlorine
\n making it unavailable as a disinfectant.
\n4) Chlorine contact time: the longer Giardia cysts are exposed to
\n chlorine, the more likely it is that the chemical will kill them.
\n5) Chlorine concentration: the higher the chlorine concentration, the
\n more likely chlorine will kill Giardia cysts. Most water treatment
\n facilities try to add enough chlorine to give a free (unbound)
\n chlorine residual at the customer tap of 0.5 mg per liter of water. <\/p>\n
The five variables above are so closely interrelated that an unfavorable
\noccurrence in one can often be compensated for by improving another. For
\nexample, if chlorine efficacy is expected to be low because water is obtained
\nfrom an icy stream, either the chlorine contact time or chlorine
\nconcentration, or both could be increased. In the case of
\nGiardia-contaminated water, it might be possible to produce safe drinking
\nwater with a chlorine concentration of 1 mg per liter and a contact time as
\nshort as 10 minutes if all the other variables were optimal (i.e., pH of 7.0,
\nwater temperature of 25 deg C, and a total organic content of the water close to
\nzero). On the other hand, if all of these variables were unfavorable (i.e.,
\npH of 7.9, water temperature of 5 deg C, and high organic content), chlorine
\nconcentrations in excess of 8 mg per liter with several hours of contact time
\nmay not be consistently effective. Because water conditions and water
\ntreatment plant operations (especially those related to water retention time
\nand, therefore, to chlorine contact time) vary considerably in different parts
\nof the United States, neither the U.S. Environmental Protection Agency nor the
\nCDC has been able to identify a chlorine concentration that would be safe yet
\neffective against Giardia cysts under all water conditions. Therefore, the
\nuse of chlorine as a preventive measure against waterborne giardiasis
\ngenerally has been used under outbreak conditions when the amount of chlorine
\nand contact time have been tailored to fit specific water conditions and the
\nexisting operational design of the water utility.<\/p>\n
In an outbreak, for example, the local health department and water utility may
\nissue an advisory to boil water, may increase the chlorine residual at the
\nconsumer’s tap from 0.5 mg per liter to 1 or 2 mg per liter, and, if the
\nphysical layout and operation of the water treatment facility permit, increase
\nthe chlorine contact time. These are emergency procedures intended to reduce
\nthe risk of transmission until a filtration device can be installed or
\nrepaired or until an alternative source of safe water, such as a well, can be
\nmade operational.<\/p>\n
The long-term solution to the problem of municipal waterborne outbreaks of
\ngiardiasis will involve improvements in and more widespread use of filters in
\nthe municipal water treatment process. The sand filters most commonly used in
\nmunicipal water treatment today cost millions of dollars to install, which
\nmakes them unattractive for many small communities. Moreover, the pore sizes
\nin these filters are not sufficiently small to remove a Giardia (6 to 9
\nmicrometers x 8 to 12 micrometers). For the sand filter to remove Giardia
\ncysts from the water effectively, the water must receive some additional
\ntreatment before it reaches the filter. In addition, the flow of water
\nthrough the filter bed must be carefully regulated.<\/p>\n
An ideal prefilter treatment for muddy water would include sedimentation (a
\nholding pond where the large suspended particles are allowed to settle out by
\nthe action of gravity) followed by flocculation or coagulation (the addition
\nof chemicals such as alum or ammonium to cause microscopic particles to clump
\ntogether). The large particles resulting from the flocculation\/coagulation
\nprocess, including Giardia cysts bound to other microparticulates, are easily
\nremoved by the sand filter. Chlorine is then added to kill the bacteria and
\nviruses that may escape the filtration process. If the water comes from a
\nrelatively clear source, chlorine may be added to the water before it reaches
\nthe filter. The point here is that successful operation of a complete water
\ntreatment facility is a complex process that requires considerable training.
\nTroubleshooting breakdowns or recognizing potential problems in the system
\nbefore they occur often requires the skills of an engineer. Unfortunately,
\nmost small water utilities that have a water treatment facility that includes
\nfiltration cannot afford the services of a full-time engineer. Filter
\noperation or maintenance problems in such systems may not be detected until a
\nGiardia outbreak is recognized in the community. The bottom line is that
\nalthough, in reference to municipal systems, water filtration is the best that
\nwater treatment technology has to offer against waterborne giardiasis, it is
\nnot infallible. For municipal water filtration facilities to work properly,
\nthey must be properly constructed, operated, and maintained.<\/p>\n
Water Disinfection in the Out-of-Doors<\/p>\n
Whenever possible, persons in the out-of-doors should carry drinking water of
\nknown purity with them. When this is not practical, and water from streams,
\nlakes, ponds, and other outdoor sources must be used, time should be taken to
\ndisinfect the water before drinking it.<\/p>\n
Boiling<\/p>\n
Boiling water is one of the simplest and most effective ways to purify water.
\nBoiling for 1 minute is adequate to kill Giardia as well as most other
\nbacterial or viral pathogens likely to be acquired from drinking polluted
\nwater.<\/p>\n
Chemical Disinfection<\/p>\n
Disinfection of water with chlorine or iodine is considered less reliable than
\nboiling for killing Giardia. However, it is recognized that boiling drinking
\nwater is not practical under many circumstances. Therefore, when one cannot
\nboil drinking water, chemical disinfectants such as iodine or chlorine should
\nbe used. This will provide some protection against Giardia and will destroy
\nmost bacteria and viruses that cause illness. Iodine or chlorine concentrations
\nof 8 mg\/liter (8ppm) with a minimum contact time of 30 minutes are recommended.
\nIf the water is cold (less than 10 deg C or 5O deg F) we suggest a minimum
\ncontact time of 60 minutes. If you have a choice of disinfectants, use iodine.
\nIodine’s disinfectant activity is less likely to be reduced by unfavorable
\nwater conditions, such as dissolved organic material in water or by water with
\na high pH, than chlorine.<\/p>\n
Below are instructions for disinfecting water using household tincture of
\niodine or chlorine bleach. If water is visibly dirty, it should first be
\nstrained through a clean cloth into a container to remove any sediment or
\nfloating matter. Then the water should be treated with chemicals as follows:<\/p>\n
IODINE<\/p>\n
Tincture of iodine from the medicine chest or first aid kit can be used to
\ntreat water. Mix thoroughly by stirring or shaking water in container and let
\nstand for 30 minutes.<\/p>\n
Tincture of Iodine Drops* to be Added per Quart or Liter
\n Clear Water Cold or Cloudy Water**<\/p>\n
2% 5 10<\/p>\n
* 1 drop = 0.05ml<\/p>\n
** Very turbid or very cold water may require prolonged contact time; let
\nstand up to several hours or even overnight.<\/p>\n
CHLORINE<\/p>\n
Liquid chlorine bleach used for washing clothes usually has 4% to 6% available
\nchlorine. The label should be read to find the percentage of chlorine in the
\nsolution and the treatment schedule below should be followed.<\/p>\n
Drops* to be Added per Quart or Liter
\nAvailable Chlorine Clear Water Cold or Cloudy Water**<\/p>\n
1% 10 20
\n 4% to 6% 2 4
\n 7% to lO% 1 2
\n Unknown 10 20<\/p>\n
* 1 drop = 0.05ml<\/p>\n
** Very turbid or very cold water may require prolonged contact time; let
\nstand up to several hours or even overnight.<\/p>\n
Mix thoroughly by stirring or shaking water in container and let stand for 30
\nminutes. A slight chlorine odor should be detectable in the water; if not,
\nrepeat the dosage and let stand for an additional 15 minutes before using.<\/p>\n
Filters<\/p>\n
Newcomers in the battle against waterborne giardiasis include a variety
\nof portable filters for field or individual use as well as some household
\nfilters. Manufacturers’ data accompanying these filters indicate that some
\ncan remove particles the size of a Giardia cyst or smaller and may be capable
\nof providing a source of safe drinking water for an individual or family
\nduring a waterborne outbreak. Such devices, if carefully selected, might also
\nbe useful in preventing giardiasis in international travelers, backpackers,
\ncampers, sportsmen, or persons who live or work in areas where water is known
\nto be contaminated.<\/p>\n
Unfortunately, there are yet few published reports in the scientific
\nliterature detailing both the methods used and the results of tests employed
\nto evaluate the efficacy of these filters against Giardia. Until more
\npublished experimental data become available, there are a few common sense
\nthings that a consumer should look for when selecting a portable or household
\nfilter. The first thing to consider is the filter media. Filters relying
\nsolely on ordinary or silver-impregnated carbon or charcoal should be avoided,
\nbecause they are not intended to prevent, destroy, or repel micro-organisms.
\nTheir principal use is to remove undesirable chemicals, odors, and very large
\nparticles such as rust or dirt.<\/p>\n
Some filters rely on chemicals such as iodide-impregnated resins to kill
\nGiardia. While properly designed and manufactured iodide-impregnated resin
\nfilters have been shown to kill many species of bacteria and virus present in
\nhuman feces, their efficacy against Giardia cysts is less well-established.
\nThe principle under which these filters operate is similar to that achieved by
\nadding the chemical disinfectant iodine to water, except that the
\nmicro-organisms in the water pass over the iodide-impregnated disinfectant as
\nthe water flows through the filter.<\/p>\n
While the disinfectant activity of iodide is not as readily affected as
\nchlorine by water pH or organic content, iodide disinfectant activity is
\nmarkedly reduced by cold water temperatures. Experiments on Giardia indicate
\nthat many of the cysts in cold water (4 deg C) remain viable after passage
\nthrough filters containing tri-iodide or penta-iodide disinfectants (28). As
\nindicated earlier, longer contact times (compared to those required to kill
\nbacteria) are required when using chemical filters to process cold water for
\nGiardia protection. Presently available chemical filters also are not
\nrecommended for muddy or very turbid water. Additionally, filters relying
\nsolely on chemical action usually give no indication to the user when
\ndisinfectant activity has been depleted.<\/p>\n
The so-called microstrainer types of filters are true filters. Manufacturer
\ndata accompanying these filters indicate that some have a sufficiently small
\npore size to physically restrict the passage of some micro-organisms through
\nthe filter. The types of filter media employed in microstraining filters
\ninclude orlon, ceramic, and proprietary materials. Theoretically, a filter
\nhaving an absolute pore size of less than 6 micrometers might be able to
\nprevent Giardia cysts of 8 to 10 micrometers in diameter from passing.
\nHowever, when used as a water sampling device during community outbreaks,
\nportable filters in the 1- to 3- micrometer range more effectively removed
\nGiardia cysts from raw water than filters with larger pore sizes. For
\neffective removal of bacterial or viral organisms which cause disease in
\nhumans, microstraining filters with pore sizes of less than 1 micrometer are
\nadvisable. However, the smaller the pores, the more quickly the filters will
\ntend to clog. To obtain maximum filter life, and as a matter of reasonable
\nprecaution, the cleanest available water source should always be used. Keep
\nin mind, however, that even sparkling, clear mountain streams can be heavily
\ncontaminated.<\/p>\n
Secondly, because infectious organisms can be concentrated on the filter
\nelement\/media, it is important to consider whether the filter element can be
\ncleaned or replaced without posing a significant health hazard to the user.
\nProperly engineered portable filters should also minimize the possibility of
\ncontaminating the “clean water side” of the filter with contaminated water
\nduring replacement or cleaning of the filter element. This is especially
\nimportant for filters used in the field where they are often rinsed or
\n“cleaned” in a stream or river that may be contaminated.<\/p>\n
Ongerth (29) recently evaluated four filters (First Need, H20K, Katadyn, the
\nPockett Purifier) for their ability to remove Giardia cysts from water. Only
\nthe First Need and Katadyn filters removed 100% of the cysts.<\/p>\n
Conclusion<\/p>\n
In conclusion, during the past fifteen years, giardiasis has been recognized
\nas one of the most frequently occurring waterborne diseases in the United
\nStates. The most common sources of water contamination include improperly
\ntreated municipal sewage, infected animals, and indiscriminate defecation by
\noutdoorsmen. Chlorine concentrations in the 0.1 mg per liter to 0.5 mg per
\nliter range are largely ineffective against Giardia at the contact times
\ncommonly employed by municipal water utilities. The long-term solution to the
\nproblem of municipal waterborne outbreaks of giardiasis will involve
\nappropriate pretreatment combined with improvements in and more widespread use
\nof filters in the municipal water treatment process. While both micrometer-
\nand submicrometer-rated filters are being employed on a limited scale for
\npersonal or household use, further evaluation of the efficacy of filters
\ndistributed by different manufacturers is needed to enable individuals and
\npublic health personnel to distinguish those that are safe and effective from
\nthose that are not.<\/p>\n
TABLE I
\n Percentage Number
\n of Patients<\/p>\n
Symptoms <\/p>\n
Diarrhea* 84 516
\n Malaise 80 56
\n Weakness 72 324
\n Abdominal cramps 63 412
\n Weight loss (O.5 – 11 kg) 63 412
\n Greasy, foul smelling stools 59 412
\n Nausea 57 444
\n Headaches 53 92
\n Anorexia 49 156
\n Abdominal bloating 45 380
\n Flatulence 41 388
\n Constipation 25 88
\n Vomiting 24 488
\n Fever 22 32<\/p>\n
Physical finding<\/p>\n
Abdomen tender to palpitation 66 92<\/p>\n
Laboratory findings
\n Blood
\n Anemia 15 124
\n Leukocytosis 9 32<\/p>\n
Stool
\n Increased mucus 56 32
\n Increased neutral fats 50 32
\n Blood 13 156<\/p>\n
* Index symptom; may be biased (upward)<\/p>\n
TABLE 1 – Based on data from Fifty diseases: Fifty Diagnoses, by M.G. Periroth
\nand D.J. Weiland.
\nYear Book Medical Publishers, Inc., Chicago, 1981, pp. 158-159. Reprinted by
\nspecial arrangement with Year Book Publishers, Inc.<\/p>\n
References<\/p>\n
1. Craun, Gunther T. Waterborne Giardiasis in the United States: A review.
\n American Journal of Public Health 69:817-819, 1979. <\/p>\n
2. Weller, Peter F. Intestinal Protozoa: Giardiasis. Scientific American
\n Medicine, 1985 <\/p>\n
3. Id. 2.<\/p>\n
4. Davidson, R.A. Issues in Clinical Parasitology: The treatment of Giardiasis.
\n Am J. Gastroenterol. 79:256-261, 2984 <\/p>\n
5. Id. 2.<\/p>\n
6. Intestinal Parasite Surveillance, Annual Summary 1978, Atlanta, Centers for
\n Disease Control, 1979. <\/p>\n
7. Walsh, J.D. Warren K. s. Selective Primary Health Care: An Interim Strategy
\n for Disease Control in developing countries. N. Engl. J. Med., 301:967-974,
\n 1979. <\/p>\n
8. Walsh, J.A. Estimating the Burden of Illness in the Tropics, In Tropical and
\n Geographic Medicine, Edited by K.S. Warren and A.F. Mahmoud, McGraw-Hill,
\n New York, 1981, pp 1073-1085.<\/p>\n
9. Weniger, B.D., Blaser, MlJ., Gedrose, J., Lippy, E.C., Juranek, D.D. an
\n Outbreak of Waterborne Giardiasis Associated with Heavy Water Runoff due to
\n Warm Weather and Volcanic Ashfall. Am. J. Public Health 78:868-872, 1983.<\/p>\n
10. Brodsky, R.E., Spencer, H.C., Schultz, M.G. Giardiasis in American
\n Travelers to the Soviet Union. J. Infect Dis. 130:319-323, 1974. <\/p>\n
11. Jokipii, L., Jokipii, A.M.M. Giardiasis in Travelers: A prospective Study.
\n J. Infect. Dis., 130:295-299, 1974.<\/p>\n
12. Black, R.E., Dykes, A.C., Anderson, K.E., Wells, J.G., Sinclair, S.P.,
\n Gary, G.W., Hatch, M.H., Gnagarosa, E.J. Handwashing to Prevent Diarrhea in
\n Day-Care Centers. Am. J. Epidemiol. 113:445-451, 1981.<\/p>\n
13. Pickering, L.K., Woodward, W.E., DuPont, H. L., Sullivan, P. Occurrence of
\n Giardia lamblia in Children in Day Care Centers. J. Pediatr. 104:522-526,
\n 1984.<\/p>\n
14. Sealy, D.P., Schuman, S.H. Endemic Giardiasis and Day Care. Pediatrics
\n 72:154-158, 1983. <\/p>\n
15. Pickering, L.K., Evans, D.G., DuPont, H.L., Vollet, J.J., III, Evans, D.J.,
\n Jr. diarrhea Caused by Shigella, Rotavirus, and Giardia in Day-care
\n Centers: Prospective Study. J. Peidatr., 99:51-56, 1981.<\/p>\n
16. Keystone, J.S., Yang, J., Grisdale, D., Harrington, M., Pillow, L.,
\n Andreychuk, R. Intestinal Parasites in Metropolitan Toronto Day-Care
\n Centres. Can J. Assoc. J. 131:733-735, 1984.<\/p>\n
17. Keystone, J.S., Kraden, S., Warren, M.R. Person-to-Person Transmission of
\n Giardia lamblia in Day-Care Nurseries. Can. Med. Assoc. J. 119:241-242,
\n 247-248, 1978.<\/p>\n
18. Rendtorff, R.C. The Experimental Transmission of Human Intestinal Protozoan
\n Parasites. II. Giardia lamblia cysts Given In Capsules, Am. J. Hygiene
\n 59:209-220, 1954.<\/p>\n
19. Water-related Disease Outbreaks Surveillance, Annual Summary 1983. Atlanta,
\n Centers for Disease Control, 1984.<\/p>\n
20. Craun, G.F. Waterborne Outbreaks of Giardiasis–Current Status in Giardia
\n and Giardiasis, edited by S.L. Erlandsen and E.A Meyer. Pleunu Press. New
\n York, 1984, pp 243-261. <\/p>\n
21. Frost, F. Plan, B., Liechty, B. Giardia Prevalence in Commercially Trapped
\n Mammals. J. Environ. Health 42:245-249.<\/p>\n
22. Id. 21.<\/p>\n
23. Id. 18.<\/p>\n
24. Bingham, A.K., Jarroll, E.L., Meyer, E.A. Radulescu, S. Introduction of
\n Giardia Excystation and the effect of Temperature on cyst Viability
\n compared by Eosin-Exclusion and In Vitro Excystation in Waterborne
\n Transmission of Giardiasis. Edited by J. Jakubowski and H. C. Hoff, U.S.
\n Environmental Protection Agency, Washington, DC, 1979, pp. 217-229.
\n EPA-600\/9-79-001. <\/p>\n
25. Jarroll, E.L., Bingham, A.K., Meyer, E.A. Effect of Chlorine on Giardia
\n lamblia Cyst Viability. Appl. Environ. Microbiol. 41:483-487, 1981.<\/p>\n
26. Jarroll, E.L., Jr., Bingham, A.K. Meyer, E.A. Inability of an Iodination
\n Method to Destroy completely Giardia Cysts in Cold Water. West J. Med.
\n 132:567-569, 1980.<\/p>\n
27. Jarroll, E.L., Jr., Bingham, A.K., Meyer, E.A. Giardia Cyst Destruction:
\n Effectiveness of Six Small-Quantity Water Disinfection Methods. Am. J.
\n Trop. Med. Hygiene 29:8-11, 1980.<\/p>\n
28. Marchin, B.L., Fina, L.R., Lambert, J.L., Fina, G.T. Effect of resin
\n disinfectants–13 and –15 on Giardia muris and giardia lamblia. Appl
\n Environ. Microbiol. 46:965-9, 1983.<\/p>\n
29. Ongerth JE, Johnson RL, Macdonald SC, Frost F, Stibbs HH. Back-country
\n water treatment to prevent giardiasis. Am J Public Health
\n 1989;79(12):1633-7. <\/p>\n
=====<\/p>\n
Back-country water treatment to prevent giardiasis.
\nJerry E. Ongerth, PhD, PE, Ron L. Johnson, Steven C Macdonald, MPH, Floyd Frost,
\nPhD, and Henry H. Stibbs, PhD<\/p>\n
American Journal of Public Health December 1989, Vol 79, No 12, pp 1633-1637.<\/p>\n
Copyright 1989 AJPH 0090-0036\/89$1.50 [used without permission]<\/p>\n
Abstract<\/p>\n
This study was conducted to provide current information on the effectiveness of
\nwater treatment chemicals and filters for control of Giardia cysts in areas
\nwhere treated water is not available. Four filters and seven chemical
\ntreatments were evaluated for both clear and turbid water at 10C. Three contact
\ndisinfection devices were also tested for cyst inactivation. Filters were
\ntested with 1-liter volumes of water seeded with 3×10^4 cysts of G. lamblia
\nproduced in gerbils inoculated with in vitro cultured trophozoites; the entire
\nvolume of filtrate was examined for cyst passage. Chemical treatments were
\nevaluated at concentrations specified by the manufacturer and for contact times
\nthat might be expected of hikers (30 minutes) and campers (eight hours, i.e.,
\novernight). Two of the four filter devices tested were 100 percent effective
\nfor Giardia cyst removal. Of the other two filters, one was 90 percent
\neffective and the other considerably less effective. Among the seven
\ndisinfection treatments, the iodine-based chemicals were all significantly more
\neffective than the chlorine-based chemicals. None of the chemical treatments
\nachieved 99.9 percent cyst inactivation with only 30-minute contact. After an
\neight-hour contact each of the iodine but none of the chlorine preparations
\nachieved at least 99.9 percent cyst inactivation. None of the contact
\ndisinfection devices provided appreciable cyst inactivation. Heating water to
\nat least 70C for 10 minutes was an acceptable alternative treatment.<\/p>\n
——————————————————————————–<\/p>\n
Introduction<\/p>\n
Giardia lamblia is the most commonly identified human intestinal parasite in the
\nUnited States. Giardiasis is commonly transmitted between humans, especially
\namong small children. lt is also transmitted in water, particularly in the
\nmountainous regions of the U.S. Since 1965, over 80 waterborne outbreaks of
\ngiardiasis have occurred in community water systems, affecting more than 20,000
\npersons (1). Giardiasis in hikers and campers has also been documented (2,3);
\nindeed, it is commonly considered a backpackers’ illness. Giardia cysts in
\nconcentrations as high as four per gallon have been detected in untreated
\nsurface water in northeastern and western states (4).<\/p>\n
Concern over waterborne transmission of Giardia has led to development of a
\nvariety of chemical disinfectants and portable filters for individual use in the
\nbackcountry. Although some information on such methods has been reported
\n(2,5,6), there is no comprehensive guide to their reliability in actually
\nremoving or inactivating Giardia cysts. We tested four commercially available
\nportable filters and one contact disinfection device for their ability to remove
\nGiardia cysts from water. We also evaluated the cysticidal effectiveness of
\nseven chemical disinfectants and three contact disinfection devices.<\/p>\n
——————————————————————————–<\/p>\n
Methods<\/p>\n
Cysts of G. lamblia were prepared for use in both the filtration and
\ndisinfection tests by propagation in gerbils inoculated with trophozoites from
\nsterile culture. Trophozoites were of two isolates: one from a beaver (Be-4
\nisolate from Alberta) and one from a human (H-2 CSU isolate from Colorado).
\nCysts were concentrated from crushed, filtered gerbil feces by flotation on zinc
\nsulfate (sp. gr. 1.18), cleaned, and stored in distilled water at 4C for up to
\n10 days before use. Similarly, G. muris cysts of an isolate originally obtained
\nfrom hamsters (7) were purified from feces of infected athymic (nu\/nu) mice and
\nstored before use. Cyst concentrations were determined with a Coulter Counter
\n(Model ZBI, Coulter Electronics, Hialeah, FL) and a haemacytometer. Except
\nwhere noted, cysts were added to water samples in concentrations of about
\n3×10^4\/ml. Cyst viability was assayed by fluorogenic staining (8) and in vitro
\nexcystation (7). In the former method, live cysts are distinguished by two
\nfluorescing dyes. One dye is fluorescein diacetate (FDA), which when absorbed
\nby cysts produces a fluorescent green only in live cysts; the second dye, either
\npropidium iodide (Pl) or ethidium bromide (EB), is excluded efficiently by live
\ncysts but absorbed by dead cysts, resulting in red fluorescence.<\/p>\n
Filter testing<\/p>\n
The following backpacker-type water filters were purchased from local retailers:
\nFirst Need Water Purification Device (First Need), General Ecology Inc.,
\nLionville, PA; H2OK Portable Drinking Water Treatment Unit Model No. 6 (H2OK),
\nBetter Living Laboratories Inc., Memphis, TN; Katadyn Pocket Filter (Katadyn),
\nKatadyn Products Inc., Wallisellen, Switzerland; and Pocket Purifier, Calco Ltd,
\nRosemont, IL. Also noted in this category is the Water Tech Water Purifier
\n(Water Purifier), Water Technologies Corp., Ann Arbor, Ml. Although it is not
\nadvertised as a filter and was not specifically tested for Giardia cyst removal,
\nwe report qualitative observations made during disinfection testing (see below)
\nbecause its configuration and mode of operation suggest that particle removal
\nmay occur. Physical and operating information provided in the filter packaging
\nis summarized in Appendix A. Each device was tested when it was new. Devices
\nthat removed all cysts when new were retested after a period of use
\napproximating several months for a regular weekend user.<\/p>\n
Each filter was prepared for testing by filtering four liters of tap water to
\npurge loose carbon particles or debris. The cyst removal performance of each
\nfilter was determined by filtering one liter of spring water, turbidity of 0.1
\nNTU, to which formalin-fixed G. lamblia cysts had been added. The entire
\nfiltrate volume was passed through a 25-mm dia., 5-um pore size, polycarbonate
\nmembrane (Nuclepore, Pleasanton, CA). stained with EB (100 ug\/ml), and mounted
\nunder a cover slip. Cysts were counted at x250 magnification with the aid of
\nepifluorescence microscopy. A representative portion of each filter was
\nexamined to quantify cyst recovery as described previously (9). The area
\nexamined was inversely proportional to the number of cysts found and ranged from
\n3.5 percent of seeded positive control filters to 25 percent (one quadrant) of
\nfilters with cyst densities less than one per field. Total numbers of cysts
\npresent were estimated by extrapolation in direct proportion to the area
\nexamined. In extensive work on recovery of Giardia cysts using the procedures
\ndescribed above, cyst retention on the 5-um polycarbonate membrane in a single
\nfiltration step has routinely averaged 80 to 90 percent (Ongerth JE:
\nunpublished). Accordingly, the ability to identify high levels of cyst removal,
\nwhich would result in passage of very few or no cysts, is excellent. This
\nability is unaffected by the factors that contribute to lack of precision in
\ncounting large numbers of cysts on filters; such inaccuracies usually occur when
\nonly small representative subareas are examined and the total numbers are
\nestimated by extrapolation. A seeded positive control and an unseeded negative
\ncontrol were processed with each batch of filter evaluations. The cyst removal
\nperformance evaluation was replicated three times for each filter device, with
\nresults expressed as the arithmetic average and corresponding standard
\ndeviation.<\/p>\n
Contact Disinfection Testing<\/p>\n
The Water Purifier is described in packaging information as a contact
\ndisinfection device. Likewise, the H2OK and Pocket Purifier devices are
\ndescribed as providing disinfection as well as removing cysts by filtration.
\nThese devices were therefore tested for their effect on cyst viability in
\naddition to filtration efficiency. A single 500-ml sample for each device was
\nseeded with approximately 2.5 x 10^4 cysts and passed through the device.
\nFiltrate was collected and filtered as described above to recover cysts. The
\nviability of cysts was then assessed by FDA and EB staining as described below.<\/p>\n
Disinfectant Testing<\/p>\n
The cysticidal effects of seven commercially available and commonly used
\ndisinfectant preparations were tested with identical procedures. Four of the
\nproducts were iodine based: Polar Pure Water Disinfectant (Polar Pure), Polar
\nEquipment, Saratoga, CA; Coghlan’s Emergency Germicidal Drinking Water Tablets
\n(CEGDWT). Coghlan’s Ltd, Winnipeg. Canada; Potable Aqua Drinking Water
\nGermicidal Tablets (Potable Aqua), Wisconsin Pharmacal Inc., Jackson, WI; and 2
\npercent iodine prepared from I2 reagent grade (Baker, Phillipsburg, NJ). The
\nremaining three products were chlorine-based: Sierra Water Purifier (Sierra), 4
\nin 1 Water Co., Santa Fe, NM; Halazone, Abbott Laboratories, North Chicago, IL;
\nand commercial liquid bleach (5.25 percent sodium hypochlorite). Disinfectant
\nsolutions were characterized by pH and total halogen concentration (Appendix B),
\nthe latter being determined colorimetrically using the DPD method.<\/p>\n
Two water sources were used, one to reflect clear high-mountain conditions, the
\nother to reflect downstream, more turbid conditions. Water sources were
\ncharacterized by pH, turbidity, and free chlorine demand (Appendix C). The
\nupstream source was from a small, spring-fed tributary to the Snoqualmie River
\nnear North Bend, Washington. Samples were taken from the stream approximately
\n50 yards downstream from the spring. The downstream source was the discharge
\nfrom Lake Washington in Seattle, Washington. Samples were taken in midstream at
\nthe entrance to Portage Bay, adjacent to the University of Washington campus.
\nWater samples were prepared for testing by adding disinfectant, according to
\nmanufacturers’ instructions, to one liter of water in stoppered glass bottles
\n(Appendix B).<\/p>\n
Cysticidal properties of the chemical treatments were determined as follows.<\/p>\n
1) Water was put in 50-ml disposable plastic centrifuge tubes and placed in a
\n10C incubator.<\/p>\n
2) G. lamblia cysts were added to each test sample at time zero.<\/p>\n
3) Tubes were vortex-mixed, sampled, and returned to the incubator.<\/p>\n
4) At each sampling time, i.e., time 0, 30 minutes and 8 hours, a 10-ml sample
\nwas withdrawn; a portion was used for measuring disinfectant concentration, and
\nin the remainder the disinfectant was quenched with 0.1-mM sodium thiosulphate.<\/p>\n
5) Cysts in the quenched sample portion were exposed to aqueous solutions of the
\nviability indicators, FDA (25 ug\/ml) and EH (100 ug\/ml), filtered on to a 13-mm
\ndia. 5-um pore-size filter membrane, and rinsed with distilled water (10 ml).<\/p>\n
6) Filters were mounted on glass slides, sealed under coverslips and examined by
\nepifluorescence microscopy at x250 magnification (Model 16, Carl Zeiss, Inc.,
\nThornwood, NY) to enumerate proportions of red and green fluorescing cysts
\nindicating dead and live status, respectively. The viability baseline of the
\ncysts was established by running a control sample of untreated water seeded with
\ncysts through each test, using procedures identical to those for disinfectant-
\ntreated samples. Data are presented in terms of percent survival relative to
\nthe controls (Figure 2). The effectiveness of each disinfectant for killing
\ncysts in both upstream and downstream water was determined in triplicate, with
\nresults expressed as the arithmetic average and corresponding standard
\ndeviation.<\/p>\n
The Water Tech Water Purifier, a contact disinfectant, was also tested as a
\nchemical disinfectant. The test water was 100 ml of spring-source water seeded
\nwith Giardia cysts. The treated water was filtered, stained, and examined for
\ncyst viability as described in steps 5 and 6 above. Three replicates were
\nassayed.<\/p>\n
Heat Inactivation<\/p>\n
Inactivation of G. lamblia and G. muris cysts by heating was established as
\nfollows. Cysts were added to distilled water in 15-ml glass test tubes. The
\nseeded tubes were incubated for 10 minutes at temperatures ranging from 10C to
\n70C. Afterwards, cyst suspensions were cooled immediately by swirling in 10C
\nwater for one minute. Cyst viability was determined either by excystation or by
\nstaining. If by the latter, FDA and EB were added to the samples, the tubes
\nwere vortex-mixed, and a 1-ml aliquot was filtered through a 13-mm dia. 5-um
\npore-size filter membrane. Filters were rinsed, mounted, and examined as
\ndescribed above to enumerate the live and dead cysts.<\/p>\n
——————————————————————————–<\/p>\n
Results<\/p>\n
Filter Device Tests<\/p>\n
The four filters differed significantly in their ability to remove Giardia cysts
\n(Figure 1). The number of cysts recovered from water having passed through the
\nfilter devices ranged from zero to greater than 10^4 in individual tests. The
\nperformance of individual devices was consistent as indicated by the standard
\ndeviations for each of the three replicate test sets (Figure 1). The percentage
\nof cysts removed by the devices, corresponding to 100 minus the percent of cysts
\nrecovered from the filtrate, was 100 percent for the First Need and Katadyn
\nfilters and approximately 90 percent for the H2OK filter. The concentration of
\ncysts in the Pocket Purifier effluent was not statistically different from the
\nseed concentration.<\/p>\n
The First Need and Katadyn filters were then subjected to a period of moderate
\nuse and then retested. The volume of water processed during the simulated use
\nperiod was not the same for the two filters owing to differences in their
\noperation. The difference in volume had no apparent effect on performance of
\nthe two filters. A total of 88 liters of tap water (turbidity of 0.3 NTU) was
\nfiltered with the First Need. During the process it was back-flushed, as
\nrecommended in package instructions, because the filtration rate decreased after
\n50, 71, and 75 liters had been filtered. After 88 liters had been processed,
\nthe filtration rate was about 25 percent lower than when the filter was new, and
\nit was retested in that condition. The Katadyn filter was subjected to use by
\nfiltering one liter of tap water four times a day for five days. At the end of
\neach day, the filter was cleaned according to package instructions by
\ndisassembling, brushing the filter element, and allowing it to air-dry overnight
\nbefore reassembly. After the respective periods of use, these two filters were
\ntested in triplicate for efficiency of cyst removal. Performance of these
\nfilters was the same, 100 percent cyst removal, when they were retested.<\/p>\n
Cyst Inactivation<\/p>\n
Contact Disinfection Devices – The effect of each of the contact disinfection
\ndevices on G. lamblia cyst viability was limited. The Water Purifier
\ninactivated about 15 percent of the cysts added in 100 ml of upstream (low
\nturbidity) water; the H2OK filter inactivated about 5 percent of the cyst
\nchallenge, and the Pocket Purifier inactivated about 2 percent of the cyst
\nchallenge.<\/p>\n
Chemical Disinfectants – The effectiveness of seven disinfecting chemical
\npreparations ranged from only a few percent to greater than 99.9 percent,
\ndepending on the chemical and its concentration, the contact time, and the
\ndisinfectant demand of the water (Figure 2). None of the disinfectants was more
\nthan 90 percent effective after a contact time of 30 minutes. After eight-hour
\ncontact, the four iodine-based disinfectants, each caused a greater than 99.9
\npercent reduction in viable cysts. The chlorine-based disinfectants were
\nclearly less effective than the iodine-based ones at both contact times.<\/p>\n
Heating in Water – Experiments conducted with cysts of G. lamblia and of G.
\nmuris indicated that the two species have virtually the same sensitivity to
\ninactivation by heating. Cysts at both species were completely inactivated by
\nheating to 70C for 10 minutes. Heating to 50C and 60C for 10 minutes produced
\n95 and 98 percent inactivation, respectively (Figure 3).<\/p>\n
——————————————————————————–<\/p>\n
Discussion<\/p>\n
To remove Giardia cysts from water, one must use a filter with sufficiently
\nsmall pores to trap the cysts and sufficiently large capacity to produce a
\nuseful volume of treated water before backwashing or replacement is necessary.
\nAlthough a number of manufacturers advertise that their filters remove Giardia
\ncysts, the only previously published account of filter performance was for the
\nKatadyn unit (6). Our filter evaluation study showed that only the First Need
\nand the Katadyn filters removed cysts with at least 99.9 percent effectiveness.
\nUnder the same test conditions, the H2OK filter was approximately 90 percent
\neffective and the Pocket Purifier was less than 50 percent effective for cyst
\nremoval. The analysis of viability for the cysts collected in the effluent of
\nthe Water Purifier, H2OK, and Pocket Purifier indicates that passage through the
\ndevice did not significantly reduce the percentage of viable cysts.<\/p>\n
The current study showed that none of the chemical treatments could inactivate
\nmore than 90 percent of cysts with 30 minutes of contact time at 10C. At both
\n30 minutes and eight hours of contact time, the iodine-based disinfectants
\ninactivated a higher fraction of cysts than did the chlorine-based products.
\nAll methods inactivated a lower percentage of cysts in cloudy or turbid water
\nthan in clear water. All disinfectants performed better with eight hours of
\ncontact time than with 30 minutes. Only the iodine-based compounds inactivated
\n99 to 99.9 percent of cysts, within eight hours of contact time for both turbid
\nand clear water. As observed by Jarroll, et al (5), the 2 percent tincture of
\niodine was less effective than the other iodine preparations with 30 minutes of
\ncontact time, but it was as effective as the others at eight hours. Comparison
\nof our results with those of Jarroll, et al (5), is complicated by differences
\nbetween test conditions used. However, our results generally indicate more
\nstringent requirements for effective inactivation of Giardia cysts. Differences
\nbetween cyst populations used in the two studies could account for the observed
\ndifferences, even though both were G. lamblia. Cysts produced in our
\ntrophozoite – gerbil system had consistently high intrinsic viability (>80
\npercent), excysted efficiently when fresh (80 to 90 percent), and have appeared
\nmore resistant to halogen disinfectants than reported previously (Ongerth J.E.:
\nunpublished).<\/p>\n
The results of heat inactivation in our study correspond to previous reports
\nindicating that heating to between 60C and 70C kills Giardia cysts efficiently.
\nIn addition, our data illustrate the correspondence between the fluorogenic
\nstaining and in vitro excystation procedures for assessing cyst viability. When
\napplied to cysts of the same condition. Staining indicates a slightly higher
\nproportion of viable cysts than does excystation. Overall, however, the two
\nprocedures provide comparable information.<\/p>\n
——————————————————————————–<\/p>\n
Figure 1 – Effectiveness of Four Portable Water Filters for Removal of Giardia
\nCysts from One-Liter Volumes of Water Each containing approximately 3×10^4 Cysts
\n(dotted line). [A bar chart showing the positive and negative controls and
\nresults from the filters, on a log scale. The First Need and Katadyn results
\nand the negative control were all zero. The Pocket Purifier and the positive
\ncontrol were approximately the same – i.e. the Pocket Purifier did not remove
\ncysts at all. The H2OK results were somewhat below the positive control,
\nactually — due to the log scale — indicating 90% removal.]<\/p>\n
Figure 2 – Effect of Time and Disinfectant Concentration of Seven Chemical
\nDisinfectants on Survival of G. lamblia Cysts in Turbid and in Clear Water. [A
\nrather striking bar chart comparing chemical treatments under varying
\nconditions. The chlorine compounds were basically ineffective, with no
\nsignificant effect at 30 minutes; at 8 hours the Sierra was still totally
\nineffective, the bleach killed about half the cysts, and the Halazone killed 70-
\n90% of the cysts (better in clear water). The iodine compounds were poor at 30
\nminutes in turbid water (half killed), only a little better at 30 minutes in
\nclear water (70-90% killed, with Potable Aqua the best), but completely
\neffective (100% killed) after 8 hours.]<\/p>\n
Figure 3 – Inactivation of Giardia Cysts as a Function of Temperature (10-minute
\nexposures) as Indicated by Ethidium Bromide Staining and by in vitro
\nExcystation. [A line chart showing cyst survival at different temperatures.
\nFour combinations of Giardia species, source, and laboratory technique are
\nshown, but all show approximately the same results. 40C kills no cysts; 50C
\nkills a lot of cysts, 60C kills most cysts, 70C kills all cysts.]<\/p>\n
——————————————————————————–<\/p>\n
Acknowledgements<\/p>\n
References to commercial products shall not be construed to represent or imply
\nthe approval or endorsement by project investigators or sponsors.<\/p>\n
Grant support was provided in part by the REI Environment Committee which
\nassumes no responsibility for the content of research reported in this
\nmanuscript.<\/p>\n
——————————————————————————–<\/p>\n
References<\/p>\n
(1) Craun GF: Waterborne outbreaks of giardiasis: current status. In: Erlandsen
\nSL, Meyer EA (eds): Giardia and Giardiasis. New York: Plenum Press, 1984; 243-
\n262.<\/p>\n
(2) Kahn FH, Visscher BR: Water disinfection in the wilderness. West J Med
\n1975; 122:450-453.<\/p>\n
(3) Barbour AG, Nichols CR, Fukushima T: An outbreak of giardiasis in a group of
\ncampers. Am J Trop Med Hyg 1980; 25:384-389.<\/p>\n
(4) Ongerth JE, Butler R, Donner RG, Myrick R, Merry K: Giardia cyst
\nconcentrations in river water. In: Advances in Water Treatment and Analysis,
\nVol 15. Denver: Am Water Works Assoc, 1988; 243-261.<\/p>\n
(5) Jarroll EL, Bingham AK, Meyer EA: Giardia cyst destruction: effectiveness of
\nsix small quantity water disinfection methods. Am J Trop Med Hyg 1980; 29:8-11.<\/p>\n
(6) Schmidt SD, Meier PG: Evaluation of Giardia cyst removal via portable water
\nfiltration devices. J Freshwater Ecol 1984; 2:435-439.<\/p>\n
(7) Schaefer FW III, Rice EW, Hoff JC: Factors promoting in vitro excystation of
\nGiardia muris cysts. Trans R Soc Trop Med Hyg 1984; 78:795-800.<\/p>\n
(8) Schupp DG, Erlandsen SL: A new method to determine Giardia cyst viability:
\ncorrelation of fluorescein diacetate and propidium iodide staining with animal
\ninfectivity. Appl Environ Microbiol 1987; 53:704-707.<\/p>\n
(9) Ongerth JE, Stibbs HH: Identification of Cryptosporidium oocysts in river
\nwater. Appl Environ Microbiol 1987; 53:672-676,<\/p>\n
(10) American Public Health Assoc: Chapter 408E In: Standard Methods for the
\nExamination of Water and Wastewater, 15th ed. Washington, DC: Am Public Health
\nAssoc, 1980; 309-310.<\/p>\n
——————————————————————————–<\/p>\n
Appendix A: Water Filter characteristics Listed by Manufacturers on Packaging or
\nInstruction Insert<\/p>\n
[Manufacturer column omitted. See text for this information.]<\/p>\n
Name Filter Type Operating Operating Useful Restrictions
\n Mode Rate Life \/Limitations<\/p>\n
First Need 0.4 um microscreen hand pump 1 pt\/min up to 800 A
\n plus adsorber pints<\/p>\n
H2OK 6 um mesh, 3 in. gravity 1 qt\/min 2000 gal A, B
\n activated carbon w\/Ag<\/p>\n
Katadyn 0.2 um ceramic, hand pump 1 qt\/min many years A
\nPocket Ag-impregnated
\nFilter<\/p>\n
Pocket 10 um (nominal), halo- mouth – – A
\nPurifier genated resin (38% I), suction
\n Ag-impregnated carbon<\/p>\n
Water Pur- Polystyrene resin bed gravity – 100 gal A, C
\nifier (a) (46% I2 as I5)<\/p>\n
A – Does not desalinate; not for saltwater or brackish water.
\nB – Pretreat with I2 for bacterially contaminated water.
\nC – Not for use with muddy water.
\n(a) Not described as a filter by package information.<\/p>\n
——————————————————————————–<\/p>\n
Appendix B: Characteristics of Disinfectant Preparations<\/p>\n
[Manufacturer column omitted. See text for this information.]<\/p>\n
Name Active Chemical Recommended Application Total Halogen pH
\n Concentration (b)
\n (a), (mg\/liter)<\/p>\n
Polar Pure Crystalline iodine, 1-7 capfuls per quart 2.4 (1 6.1
\n 99.5% depending on temperature cap\/quart)<\/p>\n
CEGDWT Tetraglycine hydro- 1 tablet per liter or 4.5 (1 5.6
\n periodate 16.7% (6.68% quart tab\/quart)
\n titrable iodine)<\/p>\n
Potable Tetraglycine hydro- 1 tablet per liter or 5.3 (1 5.6
\nAqua periodate 16.7% (6.68% quart tab\/quart)
\n titrable iodine)<\/p>\n
2% Iodine Iodine 0.4 ml per liter 4.5 6.5<\/p>\n
Sierra Calcium hypochlorite & 100 crystals (50 mg) 11.6 6.7
\n hydrogen peroxide Ca(OCl)2 + 6 drops H2O2
\n per gallon<\/p>\n
Halazone p-dichloro-sulfamoyl 5 tablets per quart 7.5 6.7
\n benzoic acid, 2.87%<\/p>\n
Chlorine sodium hypo-chlorite, 5 ml per gallon 3.9 7.1
\nbleach 5.25%<\/p>\n
(a) As prepared according to package instructions.
\n(b) In water treated according to package instructions.<\/p>\n
——————————————————————————–<\/p>\n
Appendix C: Characteristics of Disinfectant Test Water<\/p>\n
Source pH Turbidity (NTU) Chlorine Demand (a)
\n (mg.liter)<\/p>\n
Spring-fed 6.8 0.09 0.3<\/p>\n
Lake Washington 7.1 0.75 – 0.80 0.7<\/p>\n
(a) 30 minutes, free chlorine demand (5).<\/p>\n
——————————————————————————–<\/p>\n
The authors<\/p>\n
Address reprint requests to Jerry E. Ongerth, PhD, PE, Assistant professor,
\nDepartment of Environmental Health, SB-75, University of Washington, School of
\nPublic Health and Community Medicine, Seattle, WA 98195. Dr. Stibbs is with the
\nDepartment of Pathobiology, also at the School, and Mr. Macdonald is with the
\nDepartment of Medical Education, School of Medicine, both at the University of
\nWashington; Mr. Johnson is with the Department of Biological Chemistry, Johns
\nHopkins School of Medicine, Baltimore; Dr. Frost is with the Office of
\nEnvironmental Programs, Department of Social and Health Sciences, Olympia, WA.
\nThis paper, submitted to the Journal January 12, 1289, was revised and accepted
\nfor publication June 22, 1989.<\/p>\n
=====<\/p>\n
REI Water Filter Chart<\/p>\n
REI Water Filters Comparison Chart:
\n Katadyne MSR PUR First Need
\n————+————–+————-+————-+————+
\nMinimum | .2 absolute | .1 absolute | 1.0 nominal |.4 absolute |
\nPore Size | | | | |
\n————+————–+————-+————-+————+
\nWeight | 23 oz. | 19 oz. | 21 oz. | 14 oz. |
\n————+————–+————-+————-+————+
\nNumber of | | | | |
\nFilter | 2 | 4 | 2 | 1 |
\nElements | | | | |
\n————+————–+————-+————-+————+
\nTypes of | Screen, |Foam, Screen | Glass Fibre,| Charcoal |
\nElements | Ceramic |Carbon,Paper | Iodine resin| |
\n | |Membrane | | |
\n————+————–+————-+————-+————+
\nCost Per | $.25 | $.28 | $.24 | $.37 |
\nGallon | | | | |
\n————+————–+————-+————-+————+
\nAppr.Filter | | | | |
\nLife | 1000 | 500 | 500 | 100 |
\n(in Gallons)| | | | |
\n————+————–+————-+————-+————+
\nApproximate | | | | |
\nFiltering | 120 seconds | 90 seconds | 60 seconds | 90 seconds |
\nTime | | | | |
\n(in Quarts) | | | | |
\n————+————–+————-+————-+————+
\nCost of | | Two Parts | | |
\nReplacement | $89.00 | $20.00 & | $40.00 | $24.00 |
\nFilter | | $30.00 | | |
\n————+————–+————-+————-+————+
\nPrice | $225.00 | $140.00 | $130.00 | $37.00 |
\n————+————–+————-+————-+————+<\/p>\n
For room reasons I left off two filters. Its specs are in order:
\nBasic Designs
\n1.0 absolute, 12 oz., 2, Granular active carbin & ceramic, $.07,
\n1000, 60 MINUTES!, $40.00, $60.00.
\nTimber Line:
\n2.0 absolute, 6 oz., 1, Spun Polypro, $.30,
\n100, 70 Seconds, $??.??, $30.00.<\/p>\n
The filtering times are probably based on a new unit. Some units are
\neasy to clean, one can’t be properly, and one can be cleaned on the fly.<\/p>\n
Lower prices can be found elsewhere than REI. REI charges list mostly.<\/p>\n
Also note some units are easier to use (and clean) than others.<\/p>\n
\t Katadyn\tMSR\tPUR\t1stNeed\tline\tDesigns
\nmin pore size\t.2\t.1\t1 + I\t.4\t2\t1
\ndry weight\t23 oz\t19 oz\t21 oz\t14 oz\t6 oz\t12 oz
\nseconds\/qt\t120\t90\t60\t90\t70\tgrav-\t(when new)
\nseconds\/qt\t120\t180\t60\t180\t140\t ity\t(after usage)
\nfilter life\t1000\t500\t500\t100\t100\t1000\t(in gallons)
\ncost\/gallon\t$.25\t$.28\t$.24\t$.37\t$.30\t$.07
\nretail price\t$225\t$140\t$130\t$ 38\t$ 30\t$ 65
\nreplacement\t$ 89\t$ 50\t$ 40\t$ 24\tn\/a\t$ 40\t(filter cost)
\n# elements\t2\t4\t3\t1\t1\t2
\nelements\tscreen\tfoam\tscreen\tcarbon\tpolypro\tcarbon
\n\t\tceramic\tscreen\tglassfiber\t\tceramic
\n\t\t\tcarbon\tiodine
\n\t\t\tpaper<\/p>\n
Notes: 1st Need, Timberline, and Basic Designs require iodine to treat
\nbacteria and viruses. Katadyn and MSR require iodine to treat viruses.
\nOnly PUR requires no additional iodine. With carbon elements, only MSR,
\n1st Need, and Basic Designs remove harmful chemicals.<\/p>\n
TABLE OF CONTENTS of this chain:<\/p>\n
9\/ Water Filter wisdom
\n10\/ Words from Rachel Carson
\n11\/ Snake bite
\n12\/ Netiquette
\n13\/ Questions on conditions and travel
\n14\/ Dedication to Aldo Leopold
\n15\/ Leopold’s lot.
\n16\/ Morbid backcountry\/memorial
\n17\/ Information about bears
\n18\/ Poison ivy, frequently ask, under question
\n19\/ Lyme disease, frequently ask, under question
\n20\/ “Telling questions” backcountry Turing test
\n21\/ AMS
\n22\/ Words from Foreman and Hayduke
\n23\/ A bit of song (like camp songs)
\n24\/ What is natural?
\n25\/ A romantic notion of high-tech employment
\n26\/ Other news groups of related interest, networking
\n27\/ Films\/cinema references
\n28\/ References (written)
\n1\/ DISCLAIMER
\n2\/ Ethics
\n3\/ Learning I
\n4\/ learning II (lists, “Ten Essentials,” Chouinard comments)
\n5\/ Summary of past topics
\n6\/ Non-wisdom: fire-arms topic circular discussion
\n7\/ Phone \/ address lists
\n8\/ Fletcher’s Law of Inverse Appreciation and advice<\/p>\n
END.<\/p>\n
